Contraction device having heating control

ABSTRACT

The invention relates to a method for monitoring the temperature of the sleeve part of a tool holder, which sleeve part is inserted into the induction coil of a contraction device, wherein the instantaneous inductance of the induction coil is measured during the inductive heating and the current supply to the induction coil is influenced if the instantaneous inductance approaches, reaches, or exceeds a specified value.

BASIC SUBJECT OF THE INVENTION

The invention relates to a shrink-fit device according to the preambleto claim 1.

PRIOR ART

Shrink-fit devices for shrink-mounting and removal of tool shafts intool holders have been known for quite some time. Originally, suchshrink-fit devices were operated with a gas burner or hot air, by meansof which the sleeve part of the tool holder was heated in order to causeit to expand enough that it can accommodate or release a snugly-seatedtool shaft. Recent times have seen widespread use of shrink-fit devicesin which the respective tool holder is heated with the aid of aninduction coil. This has significantly accelerated the shrink-fittingprocess, has made it more efficient and easy to use, and has thereforecontributed to its widespread use.

The first shrink-fit device that was usable for practical applicationsis described in the patent literature by the German patent applicationDE 199 15 412.

The shrink-fit devices that have been disclosed up to this point are notoptimally automated. Errors can occur such as an excessively longinductive heating of the sleeve part of a tool holder. This can resultin an overheating of the sleeve part of the tool holder. The sleeve partis then, so to speak, unintentionally annealed. This can result in adisadvantageous change in structure. It may be necessary to discard thesleeve part and thus the entire tool holder. If the sleeve part is notimmediately discarded, there is in any case a danger that it willdevelop cracking if it is overheated multiple times.

Attempts have already been made to remedy this issue by measuring thetemperature of the sleeve part with an infrared detector or with asensor that contacts the surface of the sleeve part. The measurementwith an infrared detector depends significantly on the color and qualityof the sleeve part. Particularly after long use, the sleeve parts canexhibit certain annealing colors that distort the temperaturemeasurement. The dirt and possible residues of cooling lubricants do therest.

The contacting sensors have their own problems as well. This is becausethe precision of the temperature measurement depends among other thingson the contact intensity and also on how clean the surface of the sleevepart is.

Object of the Invention Will Be

The object of the invention, therefore, is to create a shrink-fit deviceand shrink-fitting method that is able to limit the thermal load of thesleeve part and in the ideal case, to limit it to that which isnecessary.

Attainment According to the Invention in Claim 1

According to the invention, a method for monitoring the temperature ofthe sleeve part of a tool holder that is accommodated in the inductioncoil of a shrink-fit device is proposed, which is characterized by thefollowing features: the present inductance of the induction coil ismeasured during the inductive heating and is used as a measure for theheating. The power supply to the induction coil is influenced when thepresent inductance approaches, reaches, or exceeds a predeterminedvalue. As a rule, the power supply is then switched off.

The use of the present inductance as a measure for the currenttemperature of the sleeve part has the significant advantage that theinterference variables such as color, quality, and cleanliness of thesurface of the sleeve part, which had previously distorted measurements,are completely suppressed. In comparison to previously used electricalvalues such as the measurement or calculation of the electrical energythat has been applied up to a certain point in time, the measurement ofthe present inductance has the advantage that it is significantly moreprecise. Consequently, the shrink-fit chuck is not always heated to themaximum value and for a maximum time, but instead, power is induced in acustomized way, which prevents damage to the shrink-fit chuck and mayaccelerate the re-cooling.

Other Embodiment Options

Another object of the invention is to disclose a shrink-fit device thatis significantly more compact than the previously known shrink-fitdevices and that therefore constitutes a suitable point of departure fordesigning a shrink-fit device for mobile use—ideally so that theshrink-fit device is an appliance that can be transported like a smallsuitcase, permitting the user to employ it for novel applications bysimply bringing it to a machine tool that is to undergo a tool changeand using it there so as to be able to perform a tool change on-site atthe machine.

This naturally does not exclude the possibility that the shrink-fitdevice can also be used in a conventional way in stationary fashion on acorresponding mounting device, but the mobile use is preferable.

This object is attained by means of a shrink-fit device forshrink-mounting and removal of tools equipped with a tool shaft asdescribed in connection with the main claim.

The shrink-fit device includes a tool socket, which has a sleeve partthat is open at its free end and is composed of an electricallyconductive material for accommodating the tool shaft in a frictionallyengaging fashion. The shrink-fit device also has an induction coilembodied as an annular or cylindrical coil that encompasses the sleevepart of the tool socket and is acted on by an alternating current, whichpreferably has a high frequency (and ideally, a frequency of greaterthan 1 kHz), in order to heat the sleeve part. In this case, theinduction coil has a first casing composed of magnetically conductiveand electrically nonconductive material on its outer circumference, forexample made of ferrite or of a powdered metal material. Electricallynonconductive material as defined by the invention does not necessarilyhave to be an insulator. A material is considered to be nonconductive ifthe eddy currents induced by magnetic fields only cause a slight warmingor no warming in the material. Another component of the shrink-fitdevice according to the invention is power semiconductor components forproducing an alternating current that powers the induction coil.Typically, so-called IGBTs are used for this purpose. But thyristors orMOSFETs can also be used. The shrink-fit device according to theinvention also includes an induction coil housing that is generallycomposed of plastic. Such an induction coil housing typically providesno magnetic shielding effect or at least none that is perceptible. Itssole purpose is to protect the components contained in it from externalinfluences and if possible, to simultaneously prevent the operator fromcoming into contact with voltage-carrying parts. The shrink-fit deviceaccording to the invention features the fact that the induction coil andits first casing are enclosed on the outer circumference by a secondcasing. This second casing is composed of magnetically nonconductive andelectrically conductive material. It is designed so that a possiblypresent leakage field induces electrical current in it, thus drawingenergy from the leakage field and thereby weakening the field. Thismeans that it completely eliminates or at least reduces the leakagefield situated in its vicinity to such an extent that—without furthermeasures or instead in connection with broader flanking measures—theremainder of the leakage field that is still present in its immediatevicinity is so weak that it does not exert any negative influence onpower semiconductor components situated there.

This attainment according to the invention also features the fact thatat least the power semiconductor components are accommodated togetherwith the induction coil in an induction coil housing. The induction coilhousing is preferably composed of an insulating material or is coveredwith such a material on the outside. It includes, accommodated either onits circumference side or on its interior, the following components: theinduction coil, the first and second casing of the induction coil, andat least the power semiconductor components, and preferably also thecapacitors that are positioned directly in the power circuit and/or thecontrol unit.

The term “encompassing” is understood to mean enclosing at least alongthe circumference of the induction coil. You as a rule, the inductioncoil housing will also extend into the region of the upper and lowerface and will completely or partially cover this face. It therefore hasa cup-shaped design. As a rule, the induction coil housing has no wallopenings, at least at its circumference—aside from possibly a localopening due to the function, i.e. for the supply cable and the like.

Other Embodiment Options

Preferably, the shrink-fit device is embodied so that its powersemiconductor components are accommodated directly on the outercircumference of the second casing. The expression “directly on theouter circumference” can mean with a maximum radial distance from theouter circumference surface of the second casing of the induction coilof up to approximately 60 mm or better yet, only up to 15 mm. If asecond casing is not provided, then the outer circumference surface ofthe first casing is decisive. Ideally, however, the top surfaces of thepower semiconductor components are in direct, thermally conductivecontact with the second casing, possibly with the provision of anadhesive layer. The second casing is preferably one that is embodied sothat it forms a cooling body for the power semiconductor components. Thesecond casing then absorbs the heat loss generated in the powersemiconductor components and carries it away.

It has turned out to be particularly advantageous if the second casinghas one or preferably a plurality of recesses that can each accommodatea respective power semiconductor component, preferably so that thesemiconductor component is enclosed on at least 3 sides or better still4 sides by the second casing. Such a recess in the second casing forms aregion that enjoys particular protection from the remainder of anymagnetic leakage field that is still present. This is because theleakage field lines cannot penetrate into this deeper-lying recess inwhich the power semiconductor component is positioned. They are insteadcaptured by the surrounding regions of the second casing that are higheror are situated radially further to the outside.

It has turned out to be particularly advantageous if the shrink-fitdevice, which includes at least one rectifier or at least one smoothingcapacitor as well as resonant circuit capacitors, which are involved inproducing a high-frequency alternating current inside the device forpowering the induction coil, has an induction coil around whose outercircumference the capacitors are grouped—generally so that if they areconceptually rotated around the center of the coil, the capacitors forma cylindrical ring, which encompasses the induction coil. Here, too, thecapacitors should be positioned directly on the outer circumference ofthe second casing of the induction coil. In this connection, theexpression “directly on the outer circumference” can be understood tomean a maximum radial distance of up to 125 mm, preferably of up to 40mm, measured from the outer circumference of the second casing of theinduction coil. If a second casing is not provided, then the outercircumference surface of the first casing is decisive.

A particularly advantageous embodiment of the shrink-fit device, forwhich not only dependent protection, but also independent protectionthat is not dependent on the preceding claims is claimed, is composed ofat least one induction coil for shrink-mounting and removal of toolshafts in tool holders, which coil is encompassed by a first casing,composed of magnetically conductive and electrically nonconductivematerial on its outer circumference, for example made of ferrite or of apowdered metal material; the induction coil and its first casing areencompassed by a second casing, which is composed of magneticallynonconductive and electrically conductive material. That which has beenstated above also applies to the second casing. Ideally, however, thissecond casing is designed so that under the influence of a leakage fieldof the induction coil that penetrates it, eddy currents are generated,which on the outer surface of the second casing, lead to an eliminationof the leakage field influence. In this case, it is potentially possibleto make use of the principle of so-called mutual inductance. In thesecond casing, the leakage field that penetrates it generates eddycurrents, which in turn generate an opposing field, which eliminates theinterfering leakage field, at least to the extent that powersemiconductor components can be accommodated in the vicinity of thesecond casing without suffering permanent damage.

Another particularly preferred embodiment of the shrink-fit device, forwhich not only dependent protection, but also independent protectionthat is not dependent on the preceding claims is claimed, is composed ofan induction coil for shrink-mounting and removal of tools in toolholders, which is accommodated—along with the power semiconductorcomponents that are associated with it and are necessary for producingthe alternating current, which is modified relative to the grid currentand powers the induction coil—in the induction coil housing thatencompasses it. Preferably, other components such as capacitorspositioned in power circuits and/or a rectifier and/or a transformerand/or the electronic control unit are also accommodated inside theinduction coil housing. In this embodiment, a second casing is notprovided. If need be, it can be substituted for by the fact that thepower semiconductor components and/or the control electronics and/or therectifiers each have a respective shielded housing or are accommodatedin shielded compartments. In this case, the power semiconductorcomponents are preferably actively cooled, for example with the aid of acoolant supply of the machine tool. This approach is possible with ahigher degree of complexity and is therefore included in the claimsscope.

This yields a particularly compact shrink-fit device, which is no longerdependent on a separate, more or less large switch cabinet positionednext to the shrink-fit device in which these components are separatelyaccommodated. This brings one a good deal closer to the goal of a mobileshrink-fit device.

Preferably, all of the variants of the shrink-fit device according tothe invention are designed so that the end surface of the induction coiloriented away from the tool socket is provided with a covering made of amagnetically conductive and electrically nonconductive material.

Ideally, the cover is embodied in the form of a poll shoe of the kindthat covers the entire area of the end surface of the induction coil.This is particularly important in the present context in order to keepthe outer area free of a damaging leakage field. In exceptional cases,the covering covers the entire area of the end surface of the inductioncoil if not physically, then magnetically.

It has turned out to be particularly advantageous if the cover has alocalized shielding collar in the center, close to the sleeve part, thatprotrudes in the direction of the longitudinal axis L preferably by atleast twice the amount of the tool diameter across the free end surfaceof the sleeve part of the tool holder. A shielding collar of this kindprevents the tool shaft that is close to the sleeve part from beingexposed to a damaging leakage field or being the starting point for sucha leakage field, which extends from there out into the surroundings andexerts the damaging influence, which is to be avoided, on the powersemiconductor components positioned in the immediate vicinity of theinduction coil.

It is advantageous if the end surface of the induction coil orientedtoward the tool socket is also overlapped by a magnetically conductiveand electrically nonconductive material and is preferably covered acrossits entire area except for the receiving opening for the tool holder.

In a particularly preferred embodiment, the shrink-fit device has atleast one circuit board that is positioned directly on the outercircumference of the induction coil or that predominantly or completelyencloses the outer circumference of the induction coil, preferably inthe form of a ring that is predominantly or fully self-contained in thecircumference direction and electrically contacts the capacitors and/orthe power semiconductor components positioned in the power circuit. Inthis case, the circuit board is preferably understood to be a boardapproximately 0.75 mm thick that is provided with conductor paths madeof a metallic material, but alternatively, a film equipped with metallicconductor paths can also be used. It is particularly advantageous if thecircuit board is an annular circuit board whose rotational symmetry axispreferably extends coaxially, or otherwise parallel to the longitudinalaxis of the induction coil.

Ideally, two annular circuit boards are provided, between whichcapacitors that are positioned in the power circuit are arranged alongthe circumference of the induction coil.

In a particularly preferred exemplary embodiment, the second casingforms one or more cooling ducts that preferably extend on its inside,considering the second casing as a whole. For this purpose, the secondcasing can be embodied so that it is composed of two or more parts. Theindividual parts of the casing are then sealed relative to one another.This significantly facilitates the production of internal cooling ducts.

Another particularly advantageous embodiment of the shrink-fit device,for which not only dependent protection, but also independent protectionthat is not dependent on the preceding claims is claimed, is ashrink-fit device, which features the fact that the shrink-fit devicehas a coupling for fastening the shrink-fit device to the recess of amachine tool spindle. This embodiment as well brings one significantlycloser to the goal of being able to achieve a practicably usable mobileshrink-fit device. This is because it is dangerous to work with a mobileshrink-fit device that is nearly resting freely somewhere in thevicinity of the machine tool, without somehow being reliably fastened.This problem is eliminated with the coupling according to the invention.The coupling makes it possible, after the removal of the shrink-fitchuck that is to undergo a tool change, to fasten the shrink-fit devicein its place on the machine spindle. In this case, the shrink-fit deviceis securely held for the duration of its operation and can then bequickly decoupled and removed.

In one variant, the coupling can also be used for storing the shrink-fitdevice in the tool magazine of the machine tool. From the magazine, itcan be automatically inserted into the machine spindle by the toolchanger.

In another variant, the tool changer can take the shrink-fit device fromthe tool magazine, but not insert it into the machine spindle, insteadconveying it directly to a shrink-fit socket that is clamped in themachine spindle and can shrink-mount or remove the tool. Here, too, theseparate coupling that is provided for the shrink-fit device isparticularly advantageous.

Ideally, the shrink-fit device should also be designed so that when ithas an internal cooling, it can be supplied with coolant by the coolinginductive heating of the machine tool. It is particularly advantageousto embody the shrink-fit device so that the induction coil isaccommodated with its first and, if provided, second casing and at leastwith the power semiconductor components and/or the capacitors and/orideally also the electronics for controlling the power semiconductorcomponents on the inside of a coil housing or coil housing ring, whichencompasses the circumference of the induction coil and preferably, alsoat least partially overlaps one or better two end surfaces of theinduction coil. This yields a compact unit, which possibly accommodatesall of the components that are necessary for operation and that areprotected by the shared housing from external influences and reliablyprevent the operator from coming into contact with voltage-carryingparts.

Ideally, the coil housing is provided with a plug, typically a Schukoplug (preferably in the form of a plug that is fastened to the end ofthe flexible cord) to provide a direct supply of single-phase gridalternating current from the public electrical system (preferably 110 Vor 230 V). This makes it possible to operate the shrink-fit devicevirtually anywhere. All that is needed is a standard electrical outletfor electrical appliances and if need be, a conventional extension cord.Naturally, the invention is not necessarily limited to this particularpreferred type of power supply. The power supply can also be 3-phase andbe supplied with other voltages, depending on what power is needed inthe individual case and what power supply is available at the respectivelocation. Naturally, other voltages are possible, particularly incountries that use a different grid voltage in the public electricsystem.

Alternatively, it has turned out to be particularly advantageous toprovide the shrink-fit device with a battery, which supplied with power.Such a device can also be highly mobile. The logical choice in this caseis to provide a carriage, for example in the form of a very easilymaneuverable hand truck, which carries the battery in the lower region,for example a vehicle battery, and carries the shrink-fit device in itsupper region.

Furthermore, protection is also claimed for a shrink-fit inductiveheating that is composed of a shrink-fit device of the type according tothe invention and that features the fact that the shrink-fit inductiveheating also has different coupling that can be fastened to theshrink-fit device, by means of which the shrink-fit device can befastened to the spindle of a machine tool. This makes it possible tofasten the shrink-fit device to differently equipped machine toolspindles so that it no longer matters whether the machine tool spindleis equipped for heat shrinking an HSK coupling or a machine tapercoupling, for example.

Other embodiment options, operating methods, and advantages can beinferred from the description of exemplary embodiments below with theaid of the drawings.

Between the first and second casing, preferably an intermediate casingis provided. This preferably serves as a coolant-conveying element inorder to protect the second casing and the semiconductor elementsmounted thereon from overheating. By contrast with the second casing, itis preferably not split in this case in order to ensure a simple coolantsupply. For this reason, the intermediate casing is either electrically(but not thermally) insulated relative to the second casing or iscomposed of electrically non-conductive material from the outset. Itgoes without saying that the coolant supply is sealed relative to theother components of the shrink-fit device. Alternative concepts for thecooling of the second casing without a specially embodied intermediatering are also conceivable. Naturally, this intermediate casing can alsobe embodied so that it serves as an (additional) shield.

LIST OF FIGURES

FIG. 1 shows a first exemplary embodiment in a central longitudinalsection.

FIG. 2 shows the first exemplary embodiment in a central longitudinalsection, which is rotated by 90° around the longitudinal axis L incomparison to FIG. 1.

FIG. 3 shows the first exemplary embodiment in a perspective viewobliquely from above, with the shielding collar removed.

FIG. 4 shows the first exemplary embodiment in a front view from above,with the shielding collar installed.

FIG. 5 shows the second casing of the first exemplary embodiment,equipped with power semiconductor components.

FIG. 6 shows the second exemplary embodiment, but which differs from thefirst exemplary embodiment only by means of the type of fastening to themachine tool or to the stand and in this respect, is identical withregard to the placement of the capacitors on the boards or circuitboards, which is shown here, to the first exemplary embodiment.

FIG. 7 shows the wiring diagram of a circuit for powering the inductioncoil, which according to the invention, can be used for the exemplaryembodiments.

FIG. 8 shows the different edge steepness, which is a measure for theinductance.

FIG. 9 shows a circuit arrangement of the kind that can be usedaccording to the invention in order to measure the inductance andpossibly also to automatically determine the geometry of the sleevepart.

EXEMPLARY EMBODIMENTS

FIG. 1 shows a first basic overview of the device according to theinvention.

Basic Principle of Inductive Shrink-Mounting and Removal

The drawing here clearly shows the induction coil 1 with its internalwindings 2 into the center of which a tool holder 4 is slid in order toshrink-mount or remove the holding shaft H of a tool W in the sleevepart HP. The basic function on which the shrink-mounting and removal arebased is described in greater detail in the German patent application DE199 15 412 A1. The content thereof is hereby made the subject of thisapplication.

The Shielding of the Induction Coil with Magnetically Conductive andElectrically Nonconductive Means

The present invention places high demands on the shielding of theinduction coil, even on the conventional shielding, which, by its verynature, is already known.

On its outer circumference, the induction coil is provided with a firstcasing 3 composed of electrically nonconductive and magneticallyconductive material. Typically, the first casing 3 is composed either offerrite or powdered metal or sintered metal material whose individualparticles are separated from one another in an electrically insulatingmanner and which in this way, are magnetically conductive andelectrically nonconductive. In order to prevent patent law-motivatedcircumvention attempts, it should be pointed out that in exceptionalcases, it is also conceivable instead to use a laminated casing ofcoated transformer plates, which are separated from one another byinsulating layers. In the overwhelming number of cases, such a laminatedcasing, however, does not fulfill the desired purpose.

It is particularly preferable for the first casing 3 to be embodied sothat it is completely self-contained, i.e. covers the circumferencesurface of the coil completely so that even in theory, no “magneticgaps” remain, apart from irrelevant local openings such as individualand/or small local bores or the like.

In exceptional cases, it is conceivable to embody the casing 3 so thatit is composed of individual segments that cover the circumference andhave certain open spaces between them—not shown in the figures. In somecases, such an embodiment is only barely able to function properly ifthe radial thickness of the individual segments in relation to thedimensions of the open spaces is selected to be large enough that thefield coming from the inside into the respective open space is stillattracted by the segments that are still in the vicinity of the openspace and as a result, no leakage field of any consequence can pass theopen spaces.

Preferably, the shielding composed of magnetically conductive andelectrically nonconductive material does not end with just the firstcasing.

Instead, one or better still both end surfaces of the first casing 3is/are adjoined by a magnetic cover 3 a, 3 b composed of theabove-mentioned material and these covers as a rule contact the firstcasing 3.

On the end surface of the induction coil oriented away from the toolholder, the magnetic cover 3 a is preferably embodied as a fully orpreferably partially interchangeable pole shoe, i.e. as an annularstructure with a central opening that forms a passage for the tool thatis being shrink-mounted or removed. The term “interchangeable”preferably describes a tool-free interchangeability, which is ideallycarried out with the aid of a connection that can be actuated with barehands, for example a bayonet coupling. In this way, it is possible toprocess tool holders that accept different sizes of tool shaft diameter.It is nevertheless assured that the end surface of the respective sleevepart HP comes into contact with the pole shoe on the inside of the coil.

On the end surface of the induction coil oriented toward the toolholder, the magnetic cover 3 b is preferably embodied as a flat washer,which ideally, completely overlaps the windings of the induction coiland has a central passage for the sleeve part.

For the invention, it is not in fact obligatory, but extremelyadvantageous, if the magnetic covers 3 a, 3 b provided on the endsurface (at least locally, preferably up to at least 75%, ideally allaround) protrude in the radial direction beyond the first casing 3,preferably by a radial dimension that exceeds the radial thickness ofthe first casing 3 by several times, in many cases by at least 4 times.The radial protrusion should preferably extend at an angle of 75° toideally 90° relative to the longitudinal axis L. In this way, areinforced “shielded trench,” which extends in the circumferencedirection around the coil, is produced, whose function according to theinvention will be explained in greater detail subsequently.

FIG. 1 shows a particularly preferred embodiment in which the pole shoeis composed of an annular pole piece 3 aa that remains permanently insitu and that is covered on the outside with an insulating material suchas plastic. The annular pole piece 3 aa has a shielding collar 3 abinterchangeably fastened to it. As is apparent, the annular pole piece 3aa and the shielding collar 3 ab are preferably connected to each otherwithout magnetic interruption. This is achieved in that the shieldingcollar contacts the annular pole piece, preferably by resting on it fromabove.

As is likewise shown in FIG. 1, it can be particularly advantageous if,for contacting the sleeve part, the shielding collar has a stop sectionAS that protrudes into the interior of the induction coil.

As is also clearly apparent from FIG. 1, in many cases, it isparticularly advantageous if the shielding collar is divided intoindividual segments, which can be moved obliquely, with one movementcomponent in the radial direction and one movement component in theparallel to the longitudinal axis L—so that it is possible to adjustboth the free inner diameter of the shielding collar that is availableas a tool passage and the depth with which the end of the shieldingcollar oriented toward the sleeve part protrudes into the interior ofthe induction coil.

In any case, the shielding collar ideally has a conical design or moreprecisely, has a shape that widens out in the direction of the coillongitudinal axis oriented toward the tool tip.

In order to insure the particularly high quality shielding that isdesirable for the purpose according to the invention, the shieldingcollar protrudes beyond the free end surface of the sleeve part of thetool holder in the direction of the longitudinal axis L by at leasttwice and better still by at least 2.75 times the tool diameter.

The Additional Shielding with an Electrically Conductive andMagnetically Nonconductive Material

Even a careful shielding by means of the first casing 3 and the magneticcovers 3 a, 3 b cannot prevent that a certain leakage current, which isharmful to semiconductor components, can be found at the outercircumference of the induction coil and at or in the vicinity of thecircumference surface of the first casing 3. Because of this, it is notan option to place electronic components actually in this region, whichreact sensitively to interference voltages that are induced by theleakage field. As is particularly the case with semiconductorcomponents, which constitute a significant part of the resonant circuitthat is operated close to resonance and that is used to power theinduction coil.

In order to improve the shielding even further, according to theinvention, the induction coil and its first casing 3 should be enclosedat the latter's outer circumference by a second casing 9—at least whenforgoing a cooling of the second casing—preferably so that the first andsecond casing touch each other, ideally over most or all of theircircumference surfaces that face each other.

This second casing 9 is composed of magnetically nonconductive andelectrically conductive material. The expression “electricallyconductive” here is understood to mean not only a material that iselectrically conductive on a local, so to speak “particle” level, butalso a material that permits the formation of eddy currents to an extentthat is relevant to the invention, see below.

The special thing about the second casing is that it is preferablyembodied in such a way and preferably embodied with such a thickness inthe radial direction that under the influence of the leakage field ofthe induction coil that penetrates it, eddy currents are produced in it,which bring about a weakening of the undesirable leakage field. In otherwords, this approach makes use of the principle of active shielding bymeans of an opposing field. It is therefore possible to reduce theleakage field at the outer surface of the second casing by more than50%, ideally by at least 75%. The decisive factor is that in any case,the leakage field at the surface of the second casing is reduced to suchan extent that semiconductor components can be sagely placed there. Itis crucial for this second casing to be separated from the inductioncoil both in the radial direction and magnetically by the first casingsince otherwise, it would heat up too quickly—which is not the case heresince it does not lie in the main field, but only in the leakage field.

For the term “casing” that is used in connection with the second casing,that which was defined above in connection with the first casing appliesanalogously. However, the term “casing” in connection with the secondcasing does not mean that a section of a tube that is endless in thecircumference direction has to be used. Instead, the casing ispreferably divided into individual segments that are electricallyinsulated from one another, for example by means of joints that arefilled with adhesive or plastic. This embodiment type serves to preventa series short-circuit of the kind that would result with an endlesstube section if a voltage puncture at a power semiconductor componentoccurs in the second casing and all of the power semiconductorcomponents along the second casing are at the same potential. It isimportant, however, that the individual segments are each embodied aslarge enough that the leakage field can induce field-weakening eddycurrents in them; as a result a full casing is not required in thisindividual instance; instead, it is sufficient if a conductive (withrespect to the individual circumstances) grid structure is present,which has sufficiently thick dimensions.

It should be stressed at this point that a housing, which is thin-walledin the radial direction and is only provided for the sake of mechanicalprotection, is insufficient, even if it were to be composed ofelectrically conductive material. Achieving the desired effect accordingto the invention requires a specific embodiment of the radial wallthickness of the second casing.

The preferred material for producing the second casing 9 is aluminum.

On its interior, the second casing 9 can have cooling ducts, preferablyextending in the circumference direction, optionally revolving inhelical fashion, which in the latter case, ideally form a thread.

In this case, it is particularly advantageous to embody the secondcasing 9 of two or more parts. In this case, its first part has coolingducts incorporated into its circumference, which are sealed by itssecond part.

At this point, reference should already be made to the left part of FIG.2. This part of the figure shows the coolant supply lines coolant supplylines 17, which supply the fresh coolant at the beginning of the coolantduct(s) 16 and carry away used coolant.

The Particular Positioning of the Power Semiconductor Components,Capacitors, and Possibly the Electronic Control Unit

As is clearly shown in FIG. 2 and FIG. 5, the second casing issurrounded at its circumference by the power semiconductor components10, which will be explained in greater detail below and which arepositioned directly at the outer circumference of the second casing.

In the present case, the power semiconductor components have two largemain surfaces and four small side surfaces. The large main surfaces arepreferably more than four times larger than each of the individual sidesurfaces. The power semiconductor components 10 are positioned so that aone of their large main surfaces is in a thermally conductive contactwith the second casing 9, as a rule at its outer circumference. Ideally,the appropriately large main surface of the power semiconductorcomponent 10 is glued with the aid of a thermally conductive adhesive tothe circumference surface of the second casing 9. In this case,therefore, the second casing 9 has a double function. It not onlyimproves the shielding and thus makes it possible to position powersemiconductor components in its radial vicinity (less than 10 cm awayfrom its circumference surface), it also optionally functionssimultaneously as a cooling body for the power semiconductor components.

It is particularly preferable for the second casing 9 to be providedwith recesses 11, each of which accommodates a respective powersemiconductor component, cf. FIG. 5. The figure clearly shows that therecesses 11 are ideally embodied so that they completely surround thepower semiconductor component 10 that they contain on four sides. Inthis way, the power semiconductor element 10 sits, so to speak, in asink and is thus shielded particularly well.

As is likewise clear from the figure, each of the power semiconductorcomponents 10 has three connections 12 for the voltage supply. Theconnections 12 of each power semiconductor component 10 in this caseprotrude into a region of the second casing 9 that constitutes a recess13, cf. FIG. 5. Where necessary, this optional recess 13 facilitates thewiring of the connections 12 of the respective semiconductor component10.

In the exemplary embodiment under discussion, however, that is not allthere is to the novel positioning of the power semiconductor components10. Instead, a particularly preferred embodiment is implemented here, inwhich the capacitors 14 a, 14 b are grouped around the induction coil atits outer circumference. The capacitors 14 a are preferably smoothingcapacitors which are a direct component part of the power circuit andthe capacitors 14 b are preferably resonant circuit capacitors, whichare likewise a direct component part of the power circuit. In this case,the capacitors 14 a, 14 b, if they are conceptually rotated around thecenter of the coil, form a cylindrical ring. This cylindrical ringencompasses the induction coil and preferably also the powersemiconductor components that are grouped around the latter's outercircumference. In order to electrically connect the capacitors 14 a, 14b, a plurality of electrical circuit boards 15 a, 15 b are providedwhich each enclose the outer circumference of the induction coil. Eachof these circuit boards 15 a, b preferably forms a flat washer. Each ofthe circuit boards is preferably composed of FR4 or similar materialsthat are used for circuit boards. As is clear from the drawings, theaxis of rotational symmetry of each of the two circuit boards that areembodied here as annular circuit boards, in this case coaxial to thelongitudinal axis of the coil. Each of the circuit boards is optionallyfastened to the inside of the trench in the magnetic covers 3 a, 3 b atthe place where the magnetic covers 3 a, 3 b protrude beyond the secondcasing in the radial direction.

The upper of the two electrical circuit boards 15 a supports thecapacitors—for example the smoothing capacitors 14 a or the resonantcircuit capacitors 14 b—whose terminal lugs extend through the circuitboard or are connected to the circuit board using the SMD technique sothat the smoothing capacitors hang down from the circuit board. Thelower of the two circuit boards is embodied correspondingly; thecapacitors—for example the resonant circuit capacitors 14 b or thesmoothing capacitors 14 b—protrude upward from it. On the whole, the twoelectrical circuit boards 15 a and 15 b accommodate between themselvesall of the capacitors 14 a, 14 b of the power circuit that feeds theinduction coil, viewed in the direction along the longitudinal axis ofthe induction coil.

It can therefore be said that the power semiconductors form a firstimaginary cylinder, which encompasses the induction coil and that thecapacitors 14 a, 14 b form a second imaginary cylinder, whichencompasses the first imaginary cylinder. Preferably, the capacitorsthat are only slightly sensitive to the leakage field form the imaginaryouter cylinder, while the power semiconductor components, which aredependent upon an installation space that has as weak as possible aleakage field, form the imaginary inner cylinder.

The Particular Embodiment of the Control Circuit Board or Other CircuitBoards

It can be necessary for the circuit board that supports the control unitand/or the circuit boards that contact the capacitors, which arepositioned directly in the power circuit, to be embodied as shielded.

For this purpose, preferably multi-layer circuit boards are used or theso-called multi-layer technique. In this case, two or more circuitboards are stacked on one another. The conductor paths extendpredominantly or substantially on the inside of the circuit board packetthat is produced in this way. At least one outer main surface of thecircuit board packet is metallized essentially over its entire area andtherefore serves as a shield.

The Special Supplying of the Induction Coil

It should first of all be stated as a general note that the coil shownin FIG. 1 is preferably not fully wound over its entirely length.Instead, it is preferably composed of two as a rule essentiallycylindrical winding packets. Each of these forms an end surface of theinduction coil. Preferably, the one of the two coils (in this case thelower one) is movable in the direction parallel to the longitudinal axisL and therefore can be adjusted during operation so that the only regionof the respective sleeve part that is ever heated is the one that needsto be heated. This prevents an unnecessary heating and also prevents thegeneration of an unnecessarily powerful field, which naturally has aneffect on the leakage field that is encountered. Such a coil alsocontributes to the reduction in the reactive power since it lacks thewindings in the middle region, which are not absolutely required fromthe standpoint of the most effective possible heating of the sleeve partof the tool holder, but which—when present—have a tendency to produceadditional reactive power without making a truly significantcontribution to the heating.

In order to supply the induction coil so that it produces the desiredeffect and the sleeve part of a tool holder heats up quickly enough, itis generally not sufficient to simply connect the induction coildirectly to the 50 Hz alternating current from the electrical grid.

Instead, the frequency of the voltage, voltage that is fed to the coil,must be increased. This is generally carried out electronically using afrequency converter. But if one simply powers the coil with a frequencyconverter without taking other special steps, as has occurred frequentlyin practice before now, then high reactive power losses occur.

From the standpoint of energy efficiency, these reactive power lossesare no longer relevant since the on-times in a shrink-fit device aresmall—even after a few seconds of on-time, the induction coil has heatedthe sleeve part of a tool holder enough that the tool shaft can beshrink-mounted or removed, which is why the reactive power losses havenot been perceived as undesirable before now.

The inventors have now realized that although avoiding reactive powerlosses is important since they lead to the heating of, among otherthings, the induction coil itself. In order to be able to avoid thereactive power losses, according to the invention, the induction coilmust be supplied via a resonant circuit. In the resonant circuitaccording to the invention, most of the energy required fluctuatesperiodically (at a high-frequency) back and forth between the inductioncoil and a capacitor unit. As a result, in each period—i.e.periodically—the only energy that must be replenished is that which islost to the resonant circuit by means of its heating capacity and itsother dissipation loss. The previous very high reactive power losses aretherefore eliminated. This results in the fact that the components ofthe power electronics can for the first time be miniaturized so muchthat—usually with an additional solution to the special shieldingproblem that this assembly has—they can be integrated into the coilhousing. As a result, a portable induction shrink-fit device is alreadywithin reach because its overall weight of less than 10 kg can becarried by the user to the machine tool in order to use it on site.

The power electronics feeding the induction coil are preferably embodiedas shown in FIG. 7 and are then characterized by the following features

On the input side, the power electronics is preferably fed with theuniversally available grid current NST, which in Europe is 230 V/50Hz/16 A_(max) (corresponding values in other countries e.g. 110 V in theUSA). This is possible for the first time because the previous reactivepowers are avoided, whereas before, a 380 V “three-phase current”connection. This does not rule out the possibility that under specialcircumstances a 3-phase rotary current connection will be needed, e.g.when higher power is needed. Naturally, it is possible to operate onthree-phase current even when power needs are low.

The grid current is then preferably stepped up to a higher voltage(transformer T) in order to reduce the currents that flow at apredetermined power. The current drawn from the grid is converted by therectifier G into DC current, which in turn is smoothed by the smoothingcapacitor(s) 14 a.

The actual resonant circuit SKS is fed with this DC current. Thebackbone of the resonant circuit is formed by the power semiconductorcomponents 10, the resonant circuit capacitors 14 b, and the inductioncoil 1 for the shrink-mounting and removal. The resonant circuit iscontrolled and regulated by control electronics SEK, which areessentially embodied in the form of an IC and which are fed via theirown input GNS with low-voltage DC current, which is tapped, ifnecessary, downstream of the rectifier G and the smoothing capacitor(s)14 a via a corresponding voltage divider resistor.

The power semiconductor components 10 are preferably implemented bymeans of transistors of the “Insulated-Gate Bipolar Transistor” type, orIGBTs for short.

The control electronics SEK preferably switch the IGBTs with a frequencythat dictates the working frequency that occurs in the resonant circuitSKS.

It is important that the resonant circuit SKS never operates preciselyin resonance, which lies at a phase shift between voltage U and currentI of cos φ=1. In the present case, this would lead to the rapiddestruction of the power semiconductor components 10 by the voltagepeaks. Instead, the control electronics SEK are embodied wo that theyoperate the power electronics and their resonant circuit SKS in aworking range that only lies close to resonance or the natural frequencyof the inductive heating. Preferably, the resonant circuit is controlledand regulated so that 0.9<cos φ−S 0.99. The values that lie in the rangeof 0.95−S cos φ−S 0.98 are particularly advantageous. This once againleads to an avoidance of voltage peaks and therefore further fostersminiaturization.

It should be mentioned in passing that the minimized energy consumptionmakes it possible for the first time to operate on battery power. In thesimplest case, a vehicle starter battery can be used as a suitablehigh-amperage battery.

The Particular Temperature Measurement

It is desirable provide shrink-fit devices of the species-defining typewith an optimum of operational reliability. At least, this requires anautomatic control of the heating time and/or heating capacity.

The so-called inductance u=di/dt is a characteristic value for coilsthrough which AC current flows. In shrink-fit devices of thespecies-defining type, the tool holder, which has been with its sleevepart slid into the chamber enclosed by the induction coil, constitutesan essential component of the magnetic circuit. Stated more precisely,the sleeve part constitutes the metal core of the coil. The magnitude ofthe inductance to be measured therefore depends decisively on the degreeto which the sleeve part fills the center or the so-called core, of theinduction coil, i.e. whether the relevant sleeve part has a smaller orlarger diameter or more or less mass and thus forms a smaller or largercore of the coil.

The inventor has now for the first time realized that the measurableinductance of an induction coil that is used for shrink-fitting dependsnot only on the geometry of the sleeve part, but also—in a practicallyapplicable way, also depends on the temperature of the sleeve part ofthe tool holder. The hotter the sleeve part is, the greater theinductance of the inductive heating composed of the sleeve part andinduction coil.

This is utilized according to the invention in order to improve thesafety of the shrink-fit device. The method and the use and thecorrespondingly designed shrink-fit device make use of the following:

The number of different tool holders that can possibly be used in theshrink-fit device is finite. For this reason, it is not difficult forthe manufacturer to measure and parameterize all—or at least the mostimportant—of the tool holders that are used in the shrink-fit device.Apart from this, the user can easily be told how to measure sleeve partsof tool holders that have not yet been measured and additionally storedat the factory. The device according to the invention optionally hascorresponding means or input options. In the ideal case, it uses priorparameters and a database to identify the respective contours through ameasurement and then establishes the inductance in the shrink-fit chuckused.

This measurement is carried out such that the sleeve parts of thecorresponding tool holders are inserted into the interior of theinduction coil and then a measurement is performed to determine thecurrent inductances that the inductive heating—composed of the inductioncoil and the sleeve part inserted into it—has when the sleeve part hasreached its maximum temperature. As a rule the maximum temperature isassumed to be the temperature at which the shrink-fit mounting andremoval can be optimally carried out. This prevents the sleeve part frombeing heated with unnecessary intensity and having to cool again for anunnecessarily long time. Purely for reasons of patent law or,alternatively stated, the maximum temperature may even lie somewhathigher. The maximum temperature that constitutes the threshold is thenthe maximum permissible temperature before destruction occurs, as aso-called overheating protection.

The maximum values measured in this way are stored for each tool holder,generally in the shrink-fit device or in its control unit. They remainavailable there for comparison at any time.

In order to shrink-fit a particular tool holder, the sleeve part isinserted into the induction coil and in this connection, a query isperformed as to which tool holder should now be subjected to ashrink-fitting or removal. After the user has input this information orit is has been automatically detected, then for this tool holder, theinductive heating reads out what inductance the sleeve part/inductioncoil inductive heating has when the sleeve part has reached the desiredtemperature. Then the inductive heating process is started. In thiscase, the present inductance is respectively measured. As soon as thecurrently measured present inductance approaches the threshold (i.e. thestored inductance) or this threshold is exceeded, the supply of currentto the induction coil is influenced—generally switched off or at leastreduced to a point that no damage can occur.

Preferably, care is taken to insure that the inductive heating of a toolholder, or more precisely its sleeve part, can only be started when ithas been verified that a tool holder with a cold sleeve part has in factbeen inserted into the induction coil.

In order to achieve this, a further measurement is carried out at thefactory.

This measurement is embodied such that the sleeve parts of thecorresponding tool holders are brought into the interior of theinduction coil and then a respective measurement is performed as to whatinductance the inductive heating composed of the induction coil and thesleeve part inserted into it has when the sleeve part is cold, i.e. hasbeen warmed to below 35°. The cold values that are measured in this wayare stored for each tool holder, generally in the shrink-fit device orin its control unit. They remain available there for a comparison thatis to be carried out at the start of a shrinking process.

Once the user has input—or it has been automatically detected—which toolholder with which sleeve part has been inserted into the induction coil,then the induction coil is at least briefly supplied with current andthe present inductance is measured at the same time. If it turns outthat the present inductance lies above the stored cold value, then thisis a sign that an already hot sleeve part of a tool holder is containedinside the induction coil. Then an error message is issued and/orpreferably, the heating process is not started or is aborted.

Preferably, in order to determine the inductance, the edge steepness ofthe time/current curve is measured and evaluated and used to determinethe inductance. In this regard, reference is made to FIG. 8. The lefthalf of FIG. 8 shows the time/current curve that the system composed ofthe induction coil and sleeve part exhibits when fed by a frequencyconverter with a cold sleeve part. The right half of FIG. 8 shows thetime/current curve that the system exhibits with the same amount ofpower supplied, but with a sleeve part that has been heated toshrink-fitting temperature.

A particularly useful option in connection with the temperaturemonitoring according to the invention is the automatic identification ofthe geometry of the sleeve part that has been respectively inserted intothe induction coil.

In this connection, not just the inductance, but also amount of powerconsumption by the induction coil in the course of a particular unit oftime. The decisive measure, therefore, is not the edge steepness of theindividual waves, but rather the time/current curve as a whole for aparticular time interval.

In order to determine this, a precisely operating power source is usedto output a current (test pulse) with a known current magnitude, currentshape, frequency, and duration of the impingement on the coil. Currentmagnitude is understood here to mean the maximum amplitude of thecurrent. Current shape is understood here to mean the type of ACvoltage, for example a square-wave voltage. Duration of impingement isunderstood here to mean the time during which the test pulse is output.

Depending on the diameter and mass of the relevant sleeve, it yields adifferent curve of the power consumption within the relevant unit oftime, i.e. a different time/current curve. This means that each sleevepart has a magnetic fingerprint, so to speak.

Based on this, it is once again possible to proceed in such a way thatfor all of the sleeve parts to be taken into account for processing onthe shrink-fit device, the power consumption within a particular unit oftime, i.e. the time/current curve, is measured at the factory and storedin the shrink-fit device. If the customer has then introduced aparticular sleeve part of a particular tool holder in the inductioncoil, a corresponding test pulse is output to the coil, before the startof the actual inductive heating procedure. The resulting totaltime/current curve is compared to the stored values in order to thusdetermine which sleeve part has been inserted into the induction coil.

This saves the user from having to indicate at the beginning of theinductive heating, which type of tool holder with which sleeve part hewould currently like to process with the shrink-fit device. This isinstead detected automatically. Consequently, the shrink-fit deviceaccording to the invention can automatically retrieve the storedinductance value, which is a measure for whether the inductive heatingprocedure must be terminated. At the same time, it is possible that theshrink-fit device according to the invention also automaticallyretrieves the cold value of the present inductance belonging to therelevant sleeve part and before the start of the inductive heating,determines whether the sleeve part that has been inserted into theinduction coil is even actually cold.

FIG. 9 shows how the measurements described in this section can beimplemented in terms of instrumentation. The induction coil 1 is readilyapparent here. The induction coil 1 is fed by a power source 100, whichgenerates a precisely defined test pulse, as described above. In orderto be able to produce such a test pulse with the required precision, aregulating unit 110 can be provided.

Between the two connection leads of the induction coil 1 there is ameasuring device 101, which measures the present inductance and whichcan be a measuring device of an intrinsically known design. Thismeasuring device 101 preferably includes a comparator, which comparesthe currently measured present inductance to an inductance threshold,which is a measure for whether the sleeve part has been heated enough toperform a shrink-mounting or removal. Preferably, the comparator is alsoable to compare whether the currently measured cold value of the presentinductance corresponds to the cold value of the inductance that thesleeve part that is currently inserted in the induction coil shouldhave.

An auxiliary circuit 103 is connected by means of a converter 102. Thisauxiliary circuit serves to determine what geometry the sleeve part has,which is currently inserted in the induction coil. For this purpose, theauxiliary circuit has at least one precision capacitor 104 and at leastone measuring device 105. The measuring device 105 is able to measurethe present voltage that is present via the capacitor. The auxiliarycircuit also generally has a discharging resistor 106, which istypically connected to ground and insures that the discharging resistoris discharged again after a test cycle, with the resistance beingselected to be high enough that it does not disadvantageously influencethe actual, relatively short testing cycle.

Depending on the embodiment of the sleeve part HP that is inserted intothe interior of the induction coil 1 (also see the two variants in inFIG. 9), a change occurs to the time/current curve that is exhibited bythe induction coil when it is acted on with the above-mentioned testpulse. This results in a corresponding change in the time/current curvethat is measured at the capacitor 104 by means of the measuring device105. This time/current curve is a respective fingerprint for the stateof the sleeve part.

Mobile Unit

A particular feature of the invention is that it enables for the firsttime, a mobile shrink-fit unit, which is ready for operation, generallyweighs less than 10 kg, for this reason and mostly due to its “only acoil housing with a plug” design, can be easily carried and maneuvered.For this reason, it is brought “to the machine tool” in order to be usedon-site at the location of the machine tool. It is therefore possible toleave behind the previous concept of the stationary shrink-fit machineto which the tool holders have to be delivered and from which the toolholders have to be transported once more in order to perform a toolchange and continue working.

It should first be generally noted that at least the components“induction coil, the first casing and, if provided, also the secondcasing, the power semiconductor components, and preferably also thecapacitors” are accommodated in a shared housing. Ideally, in additionto the induction coil, all of the components that are required for theoperation of the induction coil, including the control electronics, areaccommodated in a shared housing.

Preferably, the only thing leading out from the housing is a feedercable, which is used as a voltage supply to the shrink-fit device thatis formed in this way and for this purpose, ideally has a plug connectorat its end, which enables the tool-free connection to the voltagesupply. Preferably grid voltage is used here for the voltage supply, asexplained above. The end of the feeder cable is then preferable equippedwith a Schuko plug connector, which corresponds to the respectivenational requirements.

If the shrink-fit device is to be held in the hand, then centering meansare advantageously mounted on the coil housing, which facilitate thecentering of the coil relative to the axis of the tool. The centeringmeans can, for example, be embodied as radially movable fingers Fi, asshown in FIGS. 1 and 2.

It has turned out to be particularly advantageous if the device isprovided with at least one coupling KU that permits it to be coupled tothe machine tool.

As a result, the device can be easily fastened to the machine tool andthen assumes a working position that is safe and protected fromcontamination by coolant and chip particles.

This coupling KU preferably corresponds to the current coupling profilesof the kind that are used for the tool holders that are to be processedwith the shrink-fit device according to the invention, e.g. an HSKprofile, as shown by FIG. 2. In order to bring the shrink-fit deviceaccording to the invention into a safe working position all that isneeded is to uncouple the tool holder that is to undergo a tool changefrom the spindle of the machine tool and in its place, to couple theshrink-fit device with its identical coupling profile to the spindle ofthe machine tool. It is particularly advantageous if under normaloperating conditions, the coupling of the shrink-fit device can beremoved from the shrink-fit device, preferably by hand without tools(particularly by means of a bayonet coupling). The coupling of theshrink-fit device can thus easily be adapted to the coupling type beingused on the respective machine tool—machine taper coupling, HSK etc.

Ideally, the respective couplings are connected to the shrink-fit deviceaccording to the invention in such a way that cooling fluid/coolinglubricant that is output by the cooling system of the machine tool canflow through the at least one cooling duct provided in the shrink-fitdevice, preferably in its second casing—as explained above.

In this case, a cooling device—preferably one that is integrated intothe shrink-fit device (as close to the induction coil as possible)—canalso be provided. The sleeve part of the tool holder is inserted into itafter the end of the shrink-fitting procedure in order to actively coolit to a harmless contact temperature. This cooling device isadvantageously also fed by the cooling system of the machine tool,generally also via the above-mentioned coupling. Based on this,protection is also claimed for the use of the cooling fluid that isoutput from a machine tool for cooling purposes (cooling of the secondcasing and/or the tool holder) inside a shrink-fit device.

Alternatively, the shrink-fit device can also be stored in the toolmagazine of the machine tool. The tool changer can then eitherautomatically insert the shrink-fit device into the machine spindle orconvey it to a tool socket that is clamped in the spindle in order toremove or shrink-fit a tool. In the second case, the energy can besupplied via a cable, which is plugged directly into the shrink-fitdevice by means of a connector. In both cases, the shrink-fit devicedoes not have to be held by hand.

General Remarks

Protection is also claimed for those shrink-fit devices or methods oruses, which respectively have only the features of one or more of thefollowing paragraphs, regardless of features that are claimed by thecurrently cited set of claims. Furthermore, protection is also claimedfor those shrink-fit devices or methods or uses, which have the featuresof one or more of the paragraphs listed below and in addition, also haveother features from the claims that have already been proposed or therest of the description including the figures.

A shrink-fit device, which features the fact that the circuit board isan annular circuit board whose axis of rotational symmetry extendspreferably coaxially, otherwise parallel to the longitudinal axis of theinduction coil.

A shrink-fit device, which features the fact that two annular circuitboards are provided, between which the smoothing capacitors are arrangedalong the circumference of the induction coil.

A shrink-fit device, which features the fact that the second casingforms one or more cooling ducts, which preferably extend in itsinterior.

A shrink-fit device, which features the fact that the device has acoupling for fastening the device in the recess of a machine toolspindle.

A shrink-fit device, which features the fact that the shrink-fit deviceis embodied so that it can be fed with coolant by the cooling system ofthe machine tool.

A shrink-fit device, which features the fact that the inductioncoil—with its first and second casing and at least the powersemiconductor components and/or the smoothing capacitors and ideallyalso the electronics for controlling the power semiconductor componentsare accommodated on the inside of a coil housing or coil housing ring,which encompasses at least the circumference of the induction coil andpreferably also overlaps at least one, or better still both, endsurfaces of the induction coil.

A shrink-fit device, which features the fact that the coil housing has aplug for a direct feed of AC voltage from the public electrical system(110 V, 230 V, or 380 V).

A shrink-fit device, which features the fact that the shrink-fit deviceis battery-operated.

A shrink-fit device, which features the fact that a shielding collar isprovided, which is composed of individual segments that can be moved insuch a way that they can move with one movement component in the radialdirection and one movement component in the axial direction.

A shrink-fit device, which features the fact that on the end surface ofthe induction coil oriented toward the tool holder and/or in theair-filled interior of the induction coil, centering means are provided,which force a sleeve part to assume a coaxial positioning in theinduction coil, at any rate when the sleeve part has been inserted untilit has reached a stop in the induction coil.

A shrink-fit device, which features the fact that the shrink-fit devicehas at least two coil winding sections, which can be moved toward oraway from each other in the direction parallel to the longitudinal axisduring operation in order to adjust to the geometry of a sleeve partthat is to be heated.

A shrink-fit system that consists of a shrink-fit device according toone of the preceding paragraphs, which features the fact that theshrink-fit system also has numerous additional couplings that can befastened to the shrink-fit device, by means of which the shrink-fitdevice can be affixed to the spindle of a machine tool.

REFERENCE NUMERAL LIST

-   1 induction coil-   2 windings (electrical winding) of the induction coil-   3 first casing-   3 a end-surface magnetic cover, preferably in the form of a pole    shoe-   3 aa annular pole piece-   3 bb shielding collar-   3 b end-surface magnetic cover-   4 tool holder-   5 shield 5-   6 not assigned-   7 passage of the pole shoe 7-   8 not assigned-   9 second casing-   10 power semiconductor component 1-   11 recess 11-   12 connection 12 of a power semiconductor component-   13 recess of the second casing-   14 a smoothing capacitor-   14 b resonant circuit capacitor-   15 a electrical circuit board-   15 b electrical circuit board-   16 cooling duct 16-   17 cooling duct feeder line-   18-99 not assigned-   100 power source-   101 measuring device (inductance sensor)-   102 converter-   103 auxiliary circuit-   104 measurement capacitor-   105 measuring device (volt meter)-   106 discharging resistor-   107 not assigned-   108 not assigned-   109 not assigned-   110 regulating unit-   G rectifier-   GNS low-voltage DC current for supplying the control electronics-   H holding shaft of the tool-   HP sleeve part of the tool holder-   IC integrated circuit as part of the control electronics-   KU coupling for coupling the shrink-fit device to a machine tool-   L longitudinal axis of the induction coil and of the tool holder-   NST grid current-   SEK control electronics-   SKS resonant circuit-   T transformer-   W tool-   Fi radially movable finger for centering the sleeve part or tool    holder in the induction coil

The invention claimed is:
 1. A method for monitoring the temperature ofa sleeve part of a tool holder, which is inserted into an induction coilof a shrink-fit device, wherein present inductance of the induction coilis measured during inductive heating and current supply to the inductioncoil is influenced if the present inductance approaches, reaches, orexceeds a predetermined value; and for establishing reference data forone or more tool holders with different sleeve parts, comprises: duringa shrink-fitting procedure, heating the sleeve part of the tool holderby inductive heating with the induction coil and measuring the presentinductance of the induction coil when the sleeve part, inserted into theinduction coil, is heated enough for a shrink-mounting or removal, andstoring said present inductance of the induction coil for the toolholder with the sleeve part used in the shrink-fitting procedure whenthe sleeve part is ready for shrink-mounting or removal; and forsubsequent shrink-fitting procedures for one or more tool holders withdifferent sleeve parts, comprises: at the beginning of a newshrink-fitting procedure, performing a query to determine which toolholder with which sleeve part is inserted into the induction coil forthe shrink-mounting or removal, heating the sleeve part of the toolholder by inductive heating with the induction coil and measuring thepresent inductance of the induction coil during heating, and terminatingheating when the present inductance measured equals the storedinductance for the sleeve part of the tool holder when the sleeve partis ready for shrink-mounting or removal.
 2. The method of claim 1,wherein edge steepness of an alternating current flowing through theinduction coil is ascertained in order to determine the presentinductance of the induction coil.
 3. The method of claim 1, for one ormore tool holders with different sleeve parts wherein, a measurement istaken of the present inductance of the induction coil when the sleevepart, inserted into the induction coil, has not yet been heated and atthe beginning of a new shrink-fitting procedure, and the result thereofis stored; a query is performed as to which tool holder has beeninserted into the induction coil for shrink-mounting or removal and anerror message is issued, or heating is aborted or at least shortened, ifwhen measured the initial inductance is greater than a maximum thresholdthat the inductance is permitted to have in a cold state of the relevanttool holder and its sleeve part.
 4. The method of claim 1 for at leasttwo tool holders with different sleeve parts wherein, a measurement isperformed as to what chronological sequence of current flow occurs inthe induction coil when the sleeve part has been inserted into theinduction coil if the induction coil is acted on with a test pulse of aknown current magnitude, known current shape, known frequency, and knownon-time, and the result thereof is stored, and the measured values arecompared to the corresponding chronological sequence of the current flowfor the sleeve part of an unknown tool holder to determine the geometryof the sleeve part of the tool holder.
 5. The shrink-fit device forcarrying out the method of claim 1, wherein the shrink-fit devicecomprises: a measuring device for determining the present inductance ofthe induction coil, a memory for storing inductances that the inductioncoil exhibits when sleeve parts of known tool holders are slid into theinduction coil, and a comparator for comparing a present inductancevalue of the induction coil, which is determined for the sleeve partthat is currently being treated, to an inductance value that is storedin the memory.
 6. The shrink-fit device of claim 5 for shrink-mountingand removal of tools having a tool shaft using a tool socket, the devicecomprising: the sleeve part which is open at a free end thereof and iscomposed of an electrically conductive material for accommodating thetool shaft in a frictionally engaging fashion, the induction coil whichis embodied in the form of an annular or cylindrical coil, encompassesthe sleeve part of the tool socket, and can be acted on with analternating current to heat the sleeve part, power semiconductorcomponents for producing the alternating current that powers theinduction coil, and an induction coil housing composed of an insulatingmaterial, wherein the induction coil has a first casing composed ofmagnetically conductive and electrically nonconductive material on itsouter circumference, wherein the induction coil and its first casing areenclosed on the outer circumference by a second casing, the secondcasing composed of magnetically nonconductive and electricallyconductive material and designed so that it attracts and eliminates aleakage field occurring in its vicinity, and wherein at least the powersemiconductor components are accommodated together with the inductioncoil in the induction coil housing, and the induction coil housingencloses the induction coil, the first and second casing of theinduction coil, and the power semiconductor components at least alongthe circumference of the induction coil.
 7. The shrink-fit device ofclaim 6, wherein the power semiconductor components are accommodateddirectly on the outer circumference of the second casing.
 8. Theshrink-fit device of claim 6, wherein the second casing forms a coolingbody for the power semiconductor components.
 9. The shrink-fit device ofclaim 6, wherein the second casing has a plurality of recesses that caneach accommodate a respective power semiconductor component, so that thesemiconductor component is enclosed on four sides by the second casing.10. The shrink-fit device of claim 6, wherein the shrink-fit devicefurther comprises: a rectifier and smoothing capacitors for producing ahigh-frequency alternating current inside the device for powering thepower semiconductor components; and the smoothing capacitors may begrouped in a cylindrical annular shape around the induction coil at theouter circumference thereof.
 11. The shrink-fit device of claim 6,wherein the shrink-fit device further comprises: a rectifier andresonant circuit capacitors for producing a high-frequency alternatingcurrent inside the device for powering the power semiconductorcomponents; and the resonant circuit capacitors may be grouped in acylindrical annular shape around the induction coil at the outercircumference thereof.
 12. The shrink-fit device of claim 5, wherein:the induction coil and a first casing thereof are enclosed at the outercircumference by a second casing, the first casing is composed ofmagnetically conductive and electrically nonconductive material, and thesecond casing is composed of magnetically nonconductive and electricallyconductive material and is designed so that it attracts and eliminates aleakage field occurring in its vicinity.
 13. The shrink-fit device ofclaim 5, wherein the induction coil and power semiconductor componentsfor producing an alternating current, which is modified relative to gridcurrent and powers the induction coil, are accommodated together in aninduction coil housing.
 14. The shrink-fit device of claim 5, wherein anend surface of the induction coil oriented away from the tool socket isprovided with a cover made of a magnetically conductive and electricallynonconductive material, the cover in the form of a pole shoe that coversthe entire end surface.
 15. The shrink-fit device of claim 14, whereinthe cover has a localized shielding collar that protrudes in thedirection of the longitudinal axis by at least twice the amount of thetool diameter across the free end surface of the sleeve part of the toolholder.
 16. The shrink-fit device of claim 15, wherein the shieldingcollar can be replaced without tools.
 17. The shrink-fit device of claim5, wherein an end surface of the induction coil oriented toward the toolsocket is overlapped by a magnetically conductive and electricallynonconductive material.
 18. The shrink-fit device of claim 6, whereinthe shrink-fit device has at least one electrical circuit board whichencompasses the outer circumference of the induction coil andelectrically contacts smoothing capacitors or the power semiconductorcomponents.
 19. The shrink-fit device of claim 13, wherein theshrink-fit device has at least one electrical circuit board whichencompasses the outer circumference of the induction coil andelectrically contacts the smoothing capacitors or the powersemiconductor components.